Lost $2,300

Mt.Gox has given Mickael Saladi a rough start to his digital currency trading career. The 29-year-old Frenchman living in Miami, Fla., had four bitcoins sitting on the exchange when it went offline.

That might not sound like much, but that's $2,308 worth of bitcoins held in an account he can't reach. It was worth closer to $4,400 just a few weeks ago -- a lot for a fledgling entrepreneur.

Saladi is kicking himself for not recognizing the warning signs earlier. In late 2012, he tried to better secure his bitcoins on Mt.Gox by ordering a YubiKey, a special authentication system. But it never arrived.

"When that happened, I should have just moved my bitcoins," he said. "I have not lost complete hope, but I think there is a very low chance I will see those bitcoins again."